The objective of the research is to gain an understanding of the effect of level of protein intake on calcium metabolism in man. Efforts will be made to study the physiological mechanisms whereby high protein diets cause hypercalciuria. Four population groups, namely 1) young adult males, 2) older males and 3) pre- and 4) postmenopausal women will be studied. Subjects will be fed carefully controlled diets for varying lengths of time and will be given both low and high protein diets. Calcium, phosphorus and magnesium will be about 500, 800 and 350 mg, respectively, and will be the same at both protein intakes. Parathyroid function will be assessed directly by measuring serum parathyroid hormone levels and indirectly by determining urinary cyclic AMP. Other analyses indicative of calcium metabolism will also be made. Renal function will be examined by measuring glomerular filtration rate, calcium clearance, fractional excretion of calcium and fraction reabsorption.